This invention relates to microsurgical instruments for performing fine surgical tasks. More particularly, the invention relates to a microsurgical scissors with combined rotary action and axial biasing action for improving shearing action and durability.
Because successful microsurgery requires precision instrumentation for special surgical tasks, instrument designers and manufacturers face special problems. The microsurgical instrument must typically perform a delicate surgical task. Often it must be inserted into a small, relatively inaccessible area without itself causing trauma or displacing the position of tissues in the operating field. Because microsurgery demands the surgeon's concentrated attention, the surgical instrument must also operate simply and effectively to facilitate rather than complicate the surgeon's work. Moreover, the microsurgical instrument must not only perform its delicate operating task, but must also maintain its structural integrity. Because the instrument must be repeatedly used, its ability to maintain the proper relationship of its working parts helps to reduce hospital costs for replacing these expensive precision instruments.
One such instrument is a microsurgical scissors. The required characteristics of an ideal microsurgical scissors are illustrated by its use in arthroscopic surgery of the knee for repair of damaged meniscus pads. The operation typically uses the double-puncture technique in which two or more portals of entry (for example, anteromedial and anterolateral portals for repairing meniscus tears) allow arthroscopic viewing and dissection through one portal and retraction of loose or excised bodies through the second portal. Because this microsurgical procedure allows repair of the meniscus by a precision instrument as opposed to requiring partial or total removal as in arthrotomy, traumatic effects can be avoided.
Specifically, the size of the more conventional surgical instruments, the size of the incision, and the displacement of knee tissues necessary to reach the operating site often cause severe trauma to the patient, indeed much more severe than the trauma occasioned by meniscus repair itself. Moreover, the recovery period of an arthrotomy is measured in weeks and months, and the affected muscles, bones and skin may exhibit quadriceps inhibition, patellofemoral imbalance and painful scars, respectively.
Microsurgical procedures have been developed to redress these problems. The procedures use instruments that can reach the site of the operation through small incisions and with minimal displacement of intervening tissues. The working parts of one of these instruments, e.g. the blades of a scissors, are small and are positioned on the forward end of a narrow shaft that extends through a small portal of entry from the exterior. At the rearward end of the shaft are the control elements of the instrument, e.g. the handles of a scissors, which connect with the working parts through a linking rod within or adjacent to the shaft. Thus, the surgeon, by manipulating the control elements at a position external to the body, can perform a procedure at a remote operating site with minimal trauma to the patient.
In arthroscopic surgery, the working elements of the microsurgical scissors must be approximately 3-5 millimeters in diameter to be inserted through a small operating portal of entry. For successful surgery, the scissors must cut surely and precisely. To do so, the scissors must require only a small hand movement by the surgeon and must translate that movement to the shearing blades without altering their position in the operating field. In response, the faces of the blades must cooperate to cleanly shear, rather than tear, the meniscus.
To be practical, the microsurgical scissors must also endure post-operative cleaning, sterilizing and storing without sustaining debilitating damage. This lessens the expense of replacing the instrument and contributes to the success of the surgery by eliminating damaged instruments that complicate the surgeon's task. Particularly, the blades must continue to cooperate in their original, precise shearing relationship.
Prior microsurgical scissors have presented problems to surgeons. A number of instruments are illustrated by Rand in "Microneurosurgical Instrumentation," Microneurosurgery (1978); and by O'Connor, "Arthroscopic Surgery of the Knee," Arthroscopy and Arthrography of the Knee (1978). Other instruments are shown by White et al. (U.S. Pat. No. 3,834,021), Wallace (U.S. Pat. No. 2,691,370), and Stevenson (U.S. Pat. No. 1,754,806). These references all show a fixed blade on a forward extending shaft and a moving blade on a linking rod that moves axially with respect to the shaft. In each instrument, axial movement of the rod causes the blade attached to it to pivot in a shearing relationship with the fixed blade. Contact between the blades is maintained by tightly fastening the blades at the pivot point.
However, prior instruments suffer from a number of deficiencies, including misalignment or "play" in the blades. Significant surgical use and wear from cleaning, sterilizing and storing procedures causes such play at the pivot point. In turn, this play prevents the blades from bearing against each other at the traveling point of contact. Obviously, if the blades do not properly meet, they cannot cleanly shear; instead, they tend to tear the tissue.
With instruments like typical sewing scissors without a forward extending shaft and rod, the surgeon himself forces the blades to bear against each other at the point of contact by applying lateral pressure to the finger and thumb receiving grips of the handle. This is especially undesirable because it affects the surgeon's control required to make the cut and causes lateral movement of the blades with respect to the tissue.
Moreover, even the Wallace and Stevenson-type handle can displace the blades from the desired shearing area, since closing together the two members of the handle tends to vertically rotate the shaft, and hence the blades, of the instrument.
Further, prior art microsurgical scissors sometimes disassemble during an operation. If the pivot pin disengages from its position, the pin or a blade can fall from the instrument into the operating area, necessitating an independent recovery procedure.
Care of any microsurgical instrument is another major concern. Prior scissors, for example, can be easily bent or misaligned from mishandling during cleaning, sterilizing, and storing. Such damage can completely disable the instrument and contributes to the play or vertical displacement of the blades described above.